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Sustainability Advantage of Post-tensioning in Buildings

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Dennis Reilly's presentation of his Innovative work in Sustainable Design to the PTI (Post-Tensioning) Institute at their 2010 National Conference.

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Sustainability Advantage of Post-tensioning in Buildings

  1. 1. ® Dennis Reilly Arch/SE POSTEN Engineering Systems
  2. 2. In the last 100 years, the Population of the World has grown from 2 billion to 6.5 billion people. With the highest standard of living in the World, the United States consumes 25% of the World’s Natural Resources. If the rest of the World lived by our standards (which they trying to do), we would need 5 planet Earths to sustain us. Population growth over the last 2,000 years
  3. 3.   New Mandatory Regulations: Across the country, Cities, Counties and States are creating (& in some cases already mandating) Regulations, which require compliance with GREEN Building or LEED standards.
  4. 4. It just makes sense:   Sustainable Design of Post-tensioned Structures saves money and increases overall building efficiency;   While Sustainable Design of other structural building materials normally requires new construction methods or structural systems that lack a track record &, as a result, increase Professional Liability Risk, Sustainable Post-tensioning means simply designing efficiently to get the most from a well tested system, with a 40 year track record.
  5. 5.   Reduce the slab or beam thickness to it’s minimum;   Reduce the amount of steel used; and   With that in mind, as much as possible, promote the use of Moment Frame Structures, instead of Shear Wall Structures, which saves concrete & steel.
  6. 6.   Even an inefficient Post-tensioned structure uses less concrete & steel than Reinforced Concrete. So, shouldn’t Post-tensioning already be Sustainable?   To be honest - No!! As shown in the first slide, the Standard of Care is NOT Sustainable. Because of the cost of steel and concrete, Post-tensioning is already the Standard of Care.   What is required for Sustainability is to reduce the use of concrete & steel & maximize the efficiency of the building.
  7. 7. Carbon Footprint (How much Carbon Dioxide is released to the Environment in the manufacture, delivery of materials & long term use of the building) Solid Waste Resource Use Energy Use (aka Embodied Energy) Water Polution Air Pollution Carbon Footprint of Materials
  8. 8. Concrete: If you could reduce the thickness of a typical 150 ft x 300 ft concrete slab by just 1”, you would reduce the Carbon Emissions from it’s manufacture by the same amount as is produced by 4 automobiles in one year. Steel: Steel is the real culprit, making Conventionally Reinforced Concrete Buildings & Especially Steel Frame Buildings inherently Non-Green. Reducing Steel Use is Paramount!
  9. 9. Let’s look at a typical Interior Bay Flat Plate
  10. 10. To illustrate the stark difference between Post- tensioned Concrete & Reinforced Concrete: Compared to an Efficiently designed 8.5” thick Post-tensioned slab, the comparable Conventionally Reinforced Concrete Slab is 12” thick with a lot of rebar.
  11. 11. Span 2 – Reinf. Conc. Flat Slab Output
  12. 12. 12” CONC. SLAB W/480 FT OF #5 REBAR PER SPAN This is why we Post-tension in the first place!
  13. 13. Now - The Path to Sustainable Design: Stage One: Reduce the Amount of Concrete used. Using POSTEN Multistory, The “Auto Depth Option” automatically determines the thinnest slab section possible based upon the minimum Effective Pre-stress at the specific “User selected” spans &, with that, provides a full design.
  14. 14. POSTEN Multistory Design Procedures 1, 2 & 3 Computer Automatically produce an Input Efficient Design of the Rebar, Tendons & Drapes We will use Design Procedure 1, using Allowable Tensile Strength as our Control.
  15. 15. POSTEN Multistory Computer Input The Auto Depth Option determines the thinnest Concrete section possible & Proceeds with a full design.
  16. 16. POSTEN Multistory Computer Input To improve efficiency, we will allow the program to add pre-stress at the outer spans, if necessary.
  17. 17. POSTEN Multistory Computer Input We will start out with a 9.5” thick slab and see if we can reduce the Thickness of this slab.
  18. 18. Minimum Thickness Output The Output shows that POSTEN reduced the slab thickness from 9.5” to 8.5” (A savings of 1” in slab thickness) and proceeded with the design of the thinner slab.
  19. 19. Span 2 - Minimum Thickness Output
  20. 20. Span 2 - Minimum Thickness Output
  21. 21. Span 2 - Minimum Thickness Output
  22. 22. Now that we have reduced our Carbon Footprint, by minimizing the thickness of the slab, the Next Step, Reduce the amount of Steel used.
  23. 23. From analyzing Post-tensioning designs, we learned that at interior spans and cantilevers there are usually residual compressive stresses remaining at the tension faces. By analyzing & Balancing the Stresses in the sections, the efficiency of the tendons can be maximized, resulting in less steel.
  24. 24. POSTEN Multistory’s “Drape & Pre-stress Optimization” algorithms starts out by performing an Efficient Proportional Load Balancing Design. Once this design is completed, the program immediately proceeds with 10 cycles of balancing the stresses in the sections, thereby creating the most efficient design.
  25. 25. Since “Drape & Pre-stress Optimization” starts out with Proportional Load Balancing, the program knows how much steel was required by Proportional Load Balancing, and as a result, prints out the amount of steel saved in the process of Stress Balancing. Sometimes the savings is significant and sometimes the savings is minor. Normally, there is a savings.
  26. 26. Using the same computer input from Example 2, we need only turn off the “Auto Depth Option”, turn on the “Drape & Pre-stress Optimization Option” and re- run the program to get the Sustainable Design (with both the minimum concrete & steel).
  27. 27. Clear Auto Depth Option POSTEN Multistory Computer Input
  28. 28. POSTEN Multistory Computer Input Select “Drape & Pre-stress Optimization” & run the design.
  29. 29. This output shows the percentage of savings (9.2%) of steel that was saved by Performing Stress Balancing (above & beyond the Efficient Design produced by POSTEN’s Proportional Load Balancing). Minimum Steel Output
  30. 30. Span 2 - Minimum Steel Output
  31. 31. Span 2 - Minimum Steel Output
  32. 32. Span 2 - Minimum Steel Output
  33. 33. Our Sustainable Design Resulted from:   Determining the Thinnest Section of Slab or Beam (saving 1” in the post-tension design or saving 3.5” when compared to Conventional Reinf. Conc.)   Determining the least amount of Steel through Stress Balancing (saving an additional 9% of the steel)
  34. 34. POSTEN’s Automatic LEED Documentation SLAB OR FLAT PLATE SCHEDULE (SEE TYPICAL DETAIL FOR NOTATION) NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D s1 30.00 192.00 12.00 6#5 17#5 8#5 "D.F.L." 3#5 ENDS? NOMINAL LENGTH, "NL" 5.2 FT 9.8 FT 18.4 FT 3.6 FT 27.3 FT NONE NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D s2 32.00 192.00 12.00 17#5 15#5 6#5 "D.F.L." 2#5 ENDS? NOMINAL LENGTH, "NL" 10.2 FT 9.5 FT 17.4 FT 7.9 FT 29.3 FT NONE NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D s3 R. 32.00 192.00 12.00 15#5 17#5 6#5 "D.F.L." 2#5 ENDS? NOMINAL LENGTH, "NL" 9.5 FT 10.1 FT 17.6 FT 6.7 FT 29.3 FT NONE NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D END 30.00 192.00 12.00 17#5 42#5 8#5 "D.F.L." 3#5 ENDS? NOMINAL LENGTH, "NL" 9.7 FT 5.6 FT 18.5 FT 7.9 FT 27.3 FT NONE
  35. 35. POSTEN’s Automatic LEED Documentation SLAB OR FLAT PLATE SCHEDULE (SEE TYPICAL DETAIL FOR NOTATION) BAR LENGTHS SHOWN ARE NOMINAL LENGTHS, PRIOR TO ADDING ANCHORAGE FOR FULL BAR DEVELOPMENT. NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L1 30.00 288.00 8.50 4#5 5#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 5.3 FT 9.8 FT NONE 514.K 4.2 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L2 32.00 288.00 8.50 5#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 10.1 FT 9.5 FT NONE 439.K 7.1 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L3 32.00 288.00 8.50 4#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 9.5 FT 10.0 FT NONE 439.K 7.1 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES END 30.00 288.00 8.50 4#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 9.7 FT 6.3 FT NONE 495.K 7.1 1.4 4.6
  36. 36. POSTEN’s Automatic LEED Documentation SLAB OR FLAT PLATE SCHEDULE (SEE TYPICAL DETAIL FOR NOTATION) BAR LENGTHS SHOWN ARE NOMINAL LENGTHS, PRIOR TO ADDING ANCHORAGE FOR FULL BAR DEVELOPMENT. NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L1 30.00 288.00 8.50 4#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 5.3 FT 9.8 FT NONE 512.K 4.2 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L2 32.00 288.00 8.50 4#5 5#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 10.1 FT 9.5 FT NONE 370.K 7.1 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES L3 32.00 288.00 8.50 5#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 9.5 FT 10.0 FT NONE 370.K 7.1 1.4 7.1 NAME SPAN WIDTH DEPTH TOP LEFT TOP RIGHT BOT "BM" END DIST BOT "BX" ANCH'D BOT LEFT BOT RIGHT PRE- TENDON ORDINATES END 30.00 288.00 8.50 4#5 4#5 "D.F.L." ENDS? STRESS L. MID. R. NOMINAL LENGTH, "NL" 9.7 FT 6.3 FT NONE 475.K 7.1 1.4 4.2
  37. 37. POSTEN’s Automatic LEED Documentation Minimum Thickness Output
  38. 38. POSTEN’s Automatic LEED Documentation & Ultimately Minimum Steel Output
  39. 39. Using POSTEN Multistory, Post-tensioned Moment Frames Preserved the Historic Fabric of this National Historic Landmark. ®
  40. 40. When designing for Wind or Seismic Forces, the Post-tensioned Concrete Moment Frame Structure is the Sustainable Alternative.   Using less Steel and Concrete; and   Significantly improving overall building efficiency by eliminating shear walls.
  41. 41. To do this:   The columns must be accurately designed simultaneously with the Post-tensioned floors and roof, using the correct columns stiffness’s (not approximations);   The correct wind or seismic lateral forces (along with the P-delta magnification factors) must be inputted into the Post-tensioned floors & roof designs; and   Correct design procedures must be used to design the Moment Frame
  42. 42. To obtain the correct Lateral (Wind or Seismic) Forces, the Magnification Factors for P-Delta and/or the correct Column Stiffness’s (floor by floor) – we recommend using a Multistory Concrete Frame Analysis Program, such as:   ETABS by CSI or   EZframe by POSTEN Engineering Systems We strongly recommend against Finite Element Analysis
  43. 43. POSTEN Multistory Computer Input In this example, each floor level is designed, one level at a time, based upon the lateral forces & P-delta magnification factors from a 2nd order Multistory Frame Analysis for the full structure.
  44. 44. POSTEN Multistory Computer Input Moment Frames are designed by Activating Q5 – First Order Design Q7 - Gravity Force Design or Q9 – Second Order Design
  45. 45. POSTEN Multistory Computer Input Two additional Input Screens appear to include the Column Properties, Design Criteria, Lateral Forces & Magnification Factors For Post-tensioned Moment Frame Design.
  46. 46. POSTEN Multistory Computer Input
  47. 47. Span 1 Beam – Moment Frame Design
  48. 48. Span 2 Beam – Moment Frame Design
  49. 49. Span 3 Beam – Moment Frame Design
  50. 50. Columns – Moment Frame Design
  51. 51. POSTEN Multistory Computer Graphic Output Span 1 of 3 Post-tensioned Moment Frame
  52. 52. POSTEN Multistory Computer Graphic Output Span 2 of 3 Post-tensioned Moment Frame
  53. 53. POSTEN Multistory Computer Graphic Output Span 3 of 3 Post-tensioned Moment Frame
  54. 54. Sustainable Post-tensioning Advantages   Less Weight   Less Steel   Lower Building Height or Higher Building Volume   Lower Construction Cost   Lower Carbon Footprint   Lower Embodied Energy, Waste & Pollution
  55. 55. Despite Post-tensioning’s inherent advantages over Reinforced Concrete & Steel Frame, Sustainability additionally requires:   Minimizing Materials (i.e. conc. & steel);   Maximizing Efficiency (thin sections, stress analysis &/or moment frames); and   The Proper Documentation to back it up. Post-tensioning can provide it all – Like No Other.
  56. 56. Thank you for listening. ® Dennis Reilly Arch/SE POSTEN Engineering Systems 510-275-4750 sales@postensoft.com www.postensoft.com www.postensoft.blogspot.com

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